Solenoid-actuated valves are known and widely used in the mechanical arts and are used in a wide variety of applications. For example, solenoid-actuated valves are used in refrigerant circuits, electro-hydraulic braking systems, evaporative control systems, and in compressed air systems. Solenoid-actuated valves provide a mechanism for electronically controlling the flow of a fluid in various hydraulic and pneumatic systems.
In a conventional solenoid-actuated valve, a movable armature is slidably disposed in a chamber defining a longitudinal aperture that is surrounded in the longitudinal direction by a coil that can be energized to produce a desired magnetic field within the chamber. A magnetic pole piece is provided in one end of the chamber and a spring—for example, a coil spring—is disposed against the armature, providing an elastic force urging the armature away from the pole piece. The pole piece and the armature are made substantially from ferrous material(s), and positioned in the chamber such that when the coil is energized, the magnetic field will tend to urge the armature toward the pole piece, against the elastic force of the spring. In the desired operation, therefore, when the coil is not energized, the slideable armature is urged toward a first position away from the pole piece, and when the coil is energized, the armature is urged toward a second position, toward the pole piece. The chamber containing the armature is adapted to take advantage of the motion of the armature to open and close a valve, which may be accomplished in a variety of ways.
There are many design considerations in developing a functional solenoid-actuated valve. For example, the strength of the elastic spring and the properties of the magnetic circuit generated by the coil must be designed such that when the coil is not energized, the armature will be urged to the first position sufficiently to close (or open) the valve, and when the coil is energized the armature will be urged toward the second position with sufficient force to overcome the force of the spring and open (or close) the valve. A particularly important parameter in the design of solenoid-actuated valves is the design distance between the armature and the pole piece when the armature is in the first position, which is commonly referred to as the “magnetic gap.” The magnetic force urging the armature toward the pole piece, upon energizing the coil, drops off rapidly as the magnetic gap increases. Therefore, the magnetic gap must not be too wide. On the other hand, the magnetic gap must be wide enough to accommodate the desired movement of the armature in order to achieve the valving function. Establishing the desired magnetic gap, therefore, may require precise and expensive machining operations.
To overcome this expense, in some conventional solenoid-actuated valves the pole piece is adjustably disposed in the chamber, such that the maximum magnetic gap can be adjusted—for example, with use of a positioning set screw or with mating threads formed both on the pole piece and in some portion of the body of the valve. This positional adjustability of the pole piece has some disadvantages, however. The adjustability of the pole piece adds complexity, and therefore expense, to the valve design. Also, in some applications, the pole piece may not be readily accessible for adjustment.
Another aspect of conventional solenoid-actuated valves is the use of flux path components that typically surround the coil. The efficiency of the magnetic circuit for the solenoid can be significantly enhanced by providing a magnetic path extending generally from the pole piece along a path generally around the coil. The flux path provides a magnetically permeable path for the magnetic flux lines, thereby improving the magnetic field inside the chamber. Commonly used cylindrical flux path components, however, are difficult and expensive to fabricate. Other forms of flux paths either require assembly of multiple pieces and/or additional seals to close the pressurized chamber against leakage.
There remains a need, therefore, for reliable solenoid-operated valves that are relatively simple and inexpensive.